this application is a 35 USC 371 of Pct/JP00/08093 filed Mar. 17, 2000.
The present invention relates to a method and an apparatus to control the flatness of a metal sheet or plate through; heating the edge portions and/or the center portion of the metal sheet or plate, using a heating apparatus or heating apparatuses installed between two rolling stands of a tandem finishing mill, or at the entry to and/or the exit from a reversing finishing mill, or using a heating apparatus or heating apparatuses immediately after rolling; and successively cooling the sheet or plate after finish rolling: for eliminating edge waves occurring at the edge portions of the width direction and/or center waves occurring at the center portion of the width direction in a sheet or plate of metal such as steel, aluminum, titanium and the like result from temperature difference across its width before cooling.
Waviness (edge waves) of metal materials, especially that of steel materials, which becomes apparent when the materials are cooled at a cooling process after a rolling process, has been prevented conventionally through over-compensation of the waviness by forming moderate waviness at the width center (center waves or center buckles) at a hot rolling mill or a hot leveler after the rolling. However, waviness not corrected by this method has to be corrected separately by leveling work at a subsequent conditioning process.
Against this background, many methods to prevent the waviness of steel sheets or plates have been proposed. For instance, Japanese Unexamined Patent Publication No. H5-269527 proposes a method to control the flatness of a metal strip by: installing a tension leveler at a position where the cooling of the strip is finished but its coiling is not yet finished; installing a shape detection roll capable of measuring the transverse tension distribution of the strip at the position immediately before the final roll of the tension leveler; and changing the screw-down setting of the shape detection roll based on the metal strip flatness information detected by itself. As another example, Japanese Unexamined Patent Publication No. H10-263658 proposes a method to control the flatness of a metal strip by: calculating an elongation rate difference from flatness information given by a flatness gauge installed at the exit from a hot finishing mill and flatness information before coiling given by another flatness gauge installed at the entry to a coiler; and feeding the elongation difference information back to the roll bending control function of the hot finishing mill. Besides the above, Japanese Pat. No. 2792788 discloses an apparatus provided with a roller leveler and an edge heater installed between a roughing mill and a finishing mill for preventing the warping of the leading end of a strip.
The method to control the flatness of metal strips according to the Japanese Unexamined Patent Publications No. H5-269527 or No. H10-263658, however, uses the information of strip flatness or elongation strain difference as the basis of the flatness control, and neither of them does considers the information of the temperature distribution across the strip width. When a strip is cooled to near the room temperature during a rolling process, the transverse temperature distribution of the strip becomes even. However, since most of the strips are coiled at high temperature to obtain prescribed material quality in normal rolling practice, the transverse temperature distribution tends to be such that the temperature of the edge portions is lower than that of the center portion and temperature difference is generated. For this reason, even if the elongation strain difference is once removed by the above methcds, the temperature difference at this stage remains as thermal stress when the strips are cooled to the room. temperature, and the flatness is not finally corrected. Also, the apparatus according to the Japanese Patent No. 2792788 cannot compensate for the temperature drop at the edge portions occurring during the finish rolling and therefore the improvement of flatness after cooling cannot be expected.
The object of the present invention, which solves the problems contingent with the above conventional technologies, is to provide a method and an apparatus to control flatness, capable of improving the flatness by preventing edge waves occurring at the edge portions and center waves in a metal sheet or plate from appearing after cooling. The gist of the present invention, therefore, is as follows:
(1) A method to control the flatness of a metal sheet or plate characterized by: measuring the surface temperatures of the metal sheet or plate at the edge portions and the center portion across its width after one or more rolling passes at a tandem or reversing finishing mill; controlling the heating temperatures of the edge portions and/or the center portion based on the measured surface temperatures; and then water-cooling and/or hot-leveling the metal sheet or plate.
(2) A method to control the flatness of a metal sheet or plate characterized by: measuring the surface temperatures of the metal sheet or plate at the edge portions and the center portion across its width between two rolling stands of a tandem finishing mill; controlling the heating temperatures of the edge portions and/or the center portion based on the measured surface temperatures; and then cooling the metal sheet or plate after the finish rolling.
(3) A method to control the flatness of a metal sheet or plate characterized by: measuring the surface temperatures of the metal sheet or plate at the edge portions and the center portion across its width at the entry to and/or the exit from a reversing finishing mill; controlling the hearing temperatures of the edge portions and/or the center portion based on the measured surface temperatures; and then cooling the metal sheet or plate after the finish rolling.
(4) A method to control the flatness of a metal sheet or plate characterized by: heating the edge portions and/or the center portion in the width of the metal sheet or plate after completing hot rolling; and then water-cooling and/or hot-leveling the metal sheet or plate.
(5) A method to control the flatness of a metal sheet or plate characterized by: hot-leveling the metal sheet or plate after completing hot rolling; heating the edge portions and/or the center portion in the width of the metal sheet or plate; and then leaving it to cool naturally in normal atmosphere or cooling it with water.
(6) A method to control the flatness of a metal sheet or plate according to the item (4) or (5), characterized in that the water-cooling of the metal sheet or plate is conducted on a run out table (ROT cooling) and that the metal sheet or plate is coiled after the ROT cooling.
(7) A method to control the flatness of a metal sheet or plate according to the item (4) or (5), characterized by leaving the metal sheet or plate to cool naturally in a normal atmosphere after subjecting it to the water cooling and/or the hot leveling.
(8) A method to control the flatness of a metal sheete or plate according to the item (4) or (5), characterized by: measuring the surface temperatures of the metal sheet or plate at the edge portions and/or the center portion across its width after completing hot rolling and before heating it; and then controlling the heating temperatures of the edge portions and/or the center portion based on the measured temperatures.
(9) A method to control the flatness of a metal sheet or plate according to the item (4) or (5), characterized by controlling the heating temperatures of the edge portions of the metal sheet or plate so that the difference between the surface temperature of each edge portion measured in the range of 50 to 200 mm as edge portion and that of its center portion becomes within xc2x150xc2x0 C.
(10) A method to control the flatness of.a metal sheet or plate according to the item (4) or (5), characterized by controlling the heating temperature of the width center portion of the metal sheet or plate so that the difference between the average temperature of the width direction at the center portion of the metal sheet or plate and the temperature across the width, not exceeding the average temperature, becomes within xc2x110xc2x0 C.
(11) An apparatus to control the flatness of a metal sheet or plate characterized by having: a tandem finishing mill; a means to measure the surface temperatures of the metal sheet or plate at the edge portions and the center portion across its width installed between two rolling stands of the tandem finishing mill; a means to heat the edge portions and/or the center portion in a manner to control the heating temperatures based on the measured surface temperatures; and a means to cool the metal sheet or plate at the exit from the finishing mill.
(12) An apparatus to control the flatness of a metal sheet or plate characterized by having: a reversing finishing mill; a means to measure the surface temperatures of the metal sheet or plate at the edge portions and the center portion across its width installed at the entry to and/or the exit from the reversing finishing mill; a means to heat the edge portions and/or the center portion in a manner to control the heating temperatures based on the measured surface temperatures; and a means to cool the metal sheet or plate at the exit from both the means to measure the surface temperatures and the finishing mill.
(13) An apparatus to control the flatness of a metal sheet or plate according to the item (11) or (12), characterized in that a means to heat the edge portions and/or the center portion of the metal sheet or plate is an induction heater, a laser irradiation heater, a plasma irradiation heater or a gas combustion heater.
(14) A method to control the flatness of a metal sheet or plate according to any one of the items (1) to (3), characterized by trimming the edge portions of the metal sheet or plate, in addition to heating the edge portions, using a laser irradiation heater.
(15) A method to control the flatness of a metal sheet or plate according to any one of the items (1) to (5), characterized by transferring the metal sheet or plate while holding it with a pair or two pairs of upper and lower pinch rolls after the leading end of the metal sheet or plate has left the hot finishing mill and passed through the pinch rolls.
(16) An apparatus to control the flatness of a metal sheet or plate characterized by having an edge heater and/or a center portion heater for the metal sheet or plate between a hot finishing mill and a water cooling apparatus and/or a hot Leveler.
(17) An apparatus to control the flatness of a metal sheet or plate characterized by having an edge heater and/or a center portion heater for the metal sheet or plate at the exit from a hot leveler, which is installed at the exit from a hot finishing mill.
(18) An apparatus to control the.flatness of a metal sheet or plate according to the item (16) or (17), characterized by having a controlled cooling apparatus at the exit from the edge heater and/or the center portion heater for the metal sheet or plate.
(19) An apparatus to control the flatness of a metal sheet or plate according to any one of the items (11) to (18), characterized by having an apparatus to measure the surface temperature of the metal sheet or plate installed between the hot finishing mill, and the edge heater and/or the center portion heater for the metal sheet or plate.
(20) An apparatus to control the flatness of a metal sheet or plate according to the item (11) or (12), characterized by having at least a pair of upper and lower pinch rolls between the hot finishing mill and the edge heater and/or the center portion heater for the metal sheet or plate.
Here, the temperature of an edge portion of a metal sheet or plate is defined as the surface temperature of the metal sheet or plate at a point in the range of 50 to 200 mm from the edge.